1. Field of the Invention
Exemplary aspects of the present invention generally relate to an optical scanning apparatus and an image forming apparatus using the optical scanning apparatus.
2. Description of the Background Art
Image forming apparatuses such as a copier, a printer, and a facsimile using a photoreceptor serving as a latent image carrier have come to be known. In such an image forming apparatus, the photoreceptor is irradiated with deflected and scanned light beams corresponding to image information, thereby forming a latent image thereon. A visible image is then formed by developing the latent image.
An optical scanning apparatus that deflects and scans the light beams is generally equipped with a light source, a polygon mirror having a plurality of mirror surfaces that rotates while deflecting and scanning the light beams from the light source, and an optical element such as an imaging lens or the like that focuses the light beams deflected and scanned by the polygon mirror on the surface of the photoreceptor.
These components are installed in a housing. In order to prevent the optical devices, for example, the imaging lens, from getting contaminated with dust or other contaminants, the housing is covered and sealed with a cover member or the like.
One method of increasing a speed of forming the latent image on the photoreceptor by the optical scanning apparatus involves, for example, increasing a rotation speed of the polygon mirror. In such a method, durability of a motor that rotates the polygon mirror and material of the polygon mirror become an issue. Consequently, the speed of forming the latent image is limited.
Japanese Patent No. 2942721 discloses another example of an optical scanning apparatus which may increase the speed of forming the latent image. In the optical scanning apparatus, a so-called multi-beam optical scanning apparatus, a plurality of light beams serving as writing beams is simultaneously emitted and scans the photoreceptor.
In the multi-beam optical scanning apparatus, a resolution in a sub-scan direction is determined based on the rotation speed of the photoreceptor and a space (hereinafter referred to as a beam pitch) between each scan line of the plurality of scan lines.
However, due to variations occurring during installation when the plurality of light sources are installed in the optical scanning apparatus and/or variations in the processing of the optical element, it is difficult to obtain a predetermined beam pitch in a uniform assembly process. Consequently, upon shipment of the optical scanning apparatus or the image forming apparatus, adjustment of the beam pitch is necessary.
The optical scanning apparatus disclosed in Japanese Patent No. 2942721 includes a light source unit having the light source and a coupling lens, and an optical housing serving as an optical element unit to which an optical element as an optical scanning system is installed.
The light source unit is rotated about a rotary shaft substantially parallel to an optical axis of the light beams emitted from the light source unit relative to the optical housing to adjust the beam pitch.
The image forming apparatus including the multi-beam optical scanning apparatus is shipped after the beam pitch is adjusted. However, when the image forming apparatus is used and some parts may need to be replaced due to a failure of the light source and so forth, or when the beam pitch may need to be readjusted due to deterioration over time, the light source unit needs to be rotated in actual use to determine the position and re-adjust the beam pitch to obtain an optimal pitch.
The optical scanning apparatus disclosed in Japanese Patent No. 2942721 has a structure that allows the light source unit to rotate using a rotary driver such as a stepping motor or the like. The beam pitch can be electrically readjusted by inputting driving information of the rotary driver from an operation panel of the image forming apparatus.
However, the use of the rotary driver such as the stepping motor causes an increase in cost of the structure designated for adjustment of the beam pitch. Therefore, in order to reduce the cost, parts with relatively low reliability may be utilized in the structure for adjusting the beam pitch. Consequently, it becomes a concern that an electrical failure may occur, resulting in a permanent failure of the beam pitch adjustment.
In an attempt to solve these problems, a structure having a rotary adjusting portion that mechanically adjusts the position of the light source in a rotary direction relative to the optical housing by exerting an external force using a tool may be suggested.
When the position of the light source unit in the rotary direction relative to the optical housing can be adjusted by the tool, the rotary driver is not necessary, thereby reducing the cost of the structure dedicated to the adjustment of the beam pitch, and also preventing the permanent failure of the beam pitch adjustment.
However, in the structure mechanically allowing the adjustment of the beam pitch, the adjustment may take a significant amount of time depending on the position of the rotary adjusting portion. Consequently, the time during which the image forming apparatus is not in operation may be lengthened, resulting in poor maintenance efficiency.
Specifically, in a case in which the rotary adjusting portion is disposed at a front end surface or a lateral side surface of the optical scanning apparatus in a direction of installation of the optical scanning apparatus in the image forming apparatus, the rotary adjusting portion is inaccessible in a state in which the optical scanning apparatus is installed in the image forming apparatus.
When adjusting the beam pitch, the optical scanning apparatus needs to be partially pulled out from the image forming apparatus to a certain position so that the rotary adjusting portion becomes accessible. Alternatively, the optical scanning apparatus needs to be removed from the image forming apparatus altogether.
Either pulling out or removing the optical scanning apparatus from the image forming apparatus every time the beam pitch needs to be adjusted may prolong the time needed for beam pitch adjustment and degrade the maintenance efficiency.
It should be noted that the structure of exerting an external force to the rotary adjusting portion is not limited to the tool. In other words, a similar if not the same problem as that described above may occur when an external force is exerted on the rotary adjusting portion by a human hand.